Field of the Invention
The present invention relates to a method for generating a pattern, a storage medium, and an information processing apparatus.
Description of the Related Art
Exposure devices including an illumination optical system and a projection optical system have been used in a lithography technique. The illumination optical system illuminates a mask with light from a light source. The projection optical system projects an image of a mask pattern onto a substrate (such as a wafer). When the minimum size of the target pattern to be formed on the substrate falls below the wavelength of the light source used for the exposure, the projection of the image of the mask pattern onto the substrate involves unwanted light interaction (interference) between adjacent patterns. Thus, an unintended image, having a shape different from the target pattern, is formed on the substrate. The larger a difference between the minimum size of the target pattern and the wavelength of the light source, the higher a chance of causing defective resolution of the pattern.
One known method for generating the mask pattern using a computer includes selecting a plurality of cells from a cell library including a large number of standard cells, arranging the cells, and performing optical proximity correction (hereinafter, referred to as OPC) on the plurality of arranged cells. Through the OPC, the shape of each pattern element is corrected in such a manner that the image of the pattern is set to be within a target range. In the OPC, how the formed pattern image is affected by the interference of light between the adjacent patterns is taken into consideration. The cell library includes a plurality of cells forming a basic pattern used for the mask pattern. The plurality of cells includes patterns different from each other.
The amount of calculation for changing the shapes of the pattern elements increases along with the increase in the number of pattern elements. Thus, an extremely large amount of calculation is required when all cells to be used are arranged to generate the mask pattern and then the OPC is performed on the entire mask pattern (full chip). US Patent Application Publication No. 2009/0100396 discusses a method for addressing this situation. More specifically, the OPC is performed on the pattern in the individual cell to correct the shape of the pattern, and the plurality of cells subjected to the OPC is arranged to form the mask pattern. Then, the OPC is performed for the last time on the entire mask pattern. Since the patterns of each cell is already subjected to the OPC, the OPC on the entire mask needs not to be applied to some pattern elements having the images already corrected to be within the target range. Accordingly, the number of pattern elements to be corrected is reduced. As a result, the calculation amount in the OPC can be reduced.
In U.S. Pat. No. 7,873,929, an auxiliary pattern is arranged in a standard cell under a certain rule. Thus, the mask pattern can be generated with a smaller or no optical proximity effect produced when arranging a plurality of standard cells. In Japanese Patent Application Laid-Open No. 2005-84101, the OPC is performed with dummy patterns added on both sides of a pattern in a cell, and then the dummy patterns are removed and the resultant pattern is stored in the cell library.
US Patent Application Publication No. 2009/0100396 discusses the OPC of deforming the pattern in each cell, however, does not discuss the auxiliary pattern for achieving a higher resolution of the main pattern in a cell. Thus, the resolution improving effect of the auxiliary pattern cannot be obtained. In the U.S. Pat. No. 7,873,929, the auxiliary pattern is arranged only inside the cell. Thus, a sufficient resolution might not be achieved due to the limitation of auxiliary pattern arrangement. The dummy patterns discussed in the Japanese Patent Application Laid-Open No. 2005-84101 are placed not only in the cell but also on both sides of the cell in the OPC. The dummy patterns are removed when the cell is stored in the cell library. Thus, a sufficient resolution might not be achieved when the mask pattern is generated due to the absence of the dummy patterns in the cell selected from the cell library.